Assignment 7: Raster Data Analysis
Due March 9, 2012
Introduction
In the previous assignment you tried your hand at analyzing spatial data in vector format. Although
many GIS analytical operations can be applied to data in both spatial data models, the specifics of their
implementation could be very different.
The vector data model recreates the real world by representing its features as collections of spatially
referenced points and lines (arcs), and so the techniques used to analyze vector data are based on
geometric and/or topological transformations. In the raster model, the Earth’s surface is conceptualized
as a grid. The objects located on it are represented as single cells or groups of cells, depending on their
extent. The raster model provides for a much closer link between the spatial and aspatial characteristics
of features with the attributes stored directly in each grid cell comprising a feature. The methods used
to analyze raster data enabled by this data structure are very similar to mathematical operations
performed on matrices and are often referred to as ‘map algebra.’
This assignment will introduce you to basic analytical operations used to manipulate and integrate raster
data. The practical part of the assignment consists of the guided tutorial based on selected sections of
the ESRI web course Learning ArcGIS Spatial Analyst followed by an ‘on your own’ section.
Section 1: Theory
Textbook readings: Chapter 6 and lectures
Answers to these questions can be found in the textbook, in the guided tutorial, or online. After reading
the sources you find, please provide the answers in your own words. If you use somebody else’s
wording, please reference the source.
Each question is worth 2 marks
1. Explain why, when working with raster data, measuring distance between two points can result
in several different answers?
2. Describe possible reasons for reclassifying a raster dataset.
3. Describe the principles on which the filtering operation is based.
4. What are the issues that affect the raster overlays?
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Section 2: Guided Tutorial
This section of the assignment is based on the material of the ESRI web course Learning ArcGIS Spatial
Analyst. ArcGIS® Spatial Analyst is an ArcGIS extension that provides a set of tools for spatial analysis
and modeling. After completing this course, you will be able to:
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Understand how ArcGIS Spatial Analyst fits into the geoprocessing framework
Set up an analysis environment
Run Spatial Analyst operations using a tool dialog box and a model
Convert between feature and raster data
Reclassify data
Build Map Algebra expressions
Use Map Algebra operators
Instructions
1. Go to: http://training.esri.com and select My Training from the left-hand menu.
2. Select My Virtual Campus Courses and then log in using the username and password you created
when you worked on Assignment 1.
3. Type the course access code I sent you into the Start a New Web Course box and click Go.
4. You will see the course Learning ArcGIS Spatial Analyst appear in your course list. Click on it to
begin.
5. Save the data provided for this course on your H:\ drive or any other drive you have a permission to
write to, so that when you create or modify the datasets you would be able to save these changes.
6. In Module 1, complete all of the section Working with ArcGIS Spatial Analyst. In the section
Preparing your data for analysis, do Convert vector data to raster data and Reclassify an elevation
raster exercises.
Notes:
Exercise Work with Spatial Analyst tools
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Step 2: Enable the Spatial Analyst extension
To load the Spatial Analyst extension, from the Customize menu choose Extensions option.
When the Extensions dialog box opens, check the Spatial Analyst check box and click Close.
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Step 4: Setting the geoprocessing environment
In ArcGIS 10 the Environmental Settings dialogue box does not have the General Settings
option. All the settings mentioned in this step are represented by separate options in the
Environment Settings dialogue box. For example, you can specify the current workspace and
scratch workspace though the Workspace option. To do that, click on Workspace text to
expand this section of the dialogue box and follow the instructions in the tutorial.
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Here is how the settings in the tutorial correspond to the options you have in the ArcGIS
Environment Settings dialogue box:
Tutorial
ArcGIS 10
Current workspace
Workspace
Scratch workspace
Workspace
Extent
Processing Extent
Raster Analysis Settings
Raster Analysis
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Step 5: Run a Spatial Analyst tool from its dialog box
In ArcGIS 10 the progress of the process is tracked on the status bar at the bottom of the ArcMap
window, not in the progress window.
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Steps 6 and 7: Run a Spatial Analyst tool using the command line
We are going to skip these two steps because the changes implemented in ArcGIS 10 substantially
altered this function. In ArcGIS 10, the Command Line window has been replaced by the Python
window, where you can execute tools in command line style environment. This window can be
accessed through Geoprocessing Python. This window can also be opened by clicking on the
corresponding button on the Standard toolbar at the top of the ArcMap window. Knowledge of
Python language (or willingness and time to learn it) is required to run tools and other
functionalities from the Python window, which is outside of the scope of this class. If you would like
to learn more about Python and the Python window, please refer to the following sections in ArcGIS
Help:
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What is the Python window?
What is ArcPy?
If you would like to experiment with running tools from the Python window, open a tool’s dialogue
box and click on Tool Help button. Each article describing a tool contains sample Python scripts that
you can copy and paste into the Python window and then run.
Exercise Convert vector data to raster data
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Step 2: Set the analysis environment
To set the analysis environment, follow the notes for Step 2 in the Work with Spatial Analyst tools
exercise above.
Exercise Reclassify an elevation raster
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Step 5: Symbolize the new elevation range raster
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To see which of the colour ramps is the Surface colour ramp, right-click on a colour ramp currently
displayed in the Colour Scheme box and uncheck the Graphic View option. Now all the ramps on
the drop-down list are shown as text titles.
To change the class labels for the reclassified layer, click on the corresponding label in the
Symbology box and enter new text.
To set transparency to 45%, in the Layer Properties window switch to Display tab.
7. In Module 2, complete exercise Working with operators in the Working with operators and
functions section.
Notes:
 Step 8: ArcGIS 10 has only one ‘all purpose’ Map Algebra tool called Raster Calculator, which you
are going to use in this step.
Syntax of the expression that you need to type in the Raster Calculator box is different from
what is given in the text of the exercise:
Over("GoodFarm","Landcover")
You can copy and paste it form the text of the assignment or you can enter it in the box yourself.
If you chose latter, start by locating the OVER tool on the scroll-down list of tools on the right
side of the dialogue box. Double click on it to enter in into the expression box. Then locate the
names of the raster layers you want to perform the operation on and double-click on them to
get them entered into the box. Make sure that the layer names are entered between the round
brackets and are separated by the comma.
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Step 9: Find differences between the NewLand and the Landcover layers
The expression you need to enter in this step is
Diff("Landcover","NewLand")
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Step 10: Find suitable soils
The expression you need to enter in this step is
InList("Soils",[201, 204])
The InList tool is part of the Logical group of tool at the bottom of the scroll-down list on the
right side of the Raster Calculator dialogue box. You can also find them as separate tool
included in the Math Logical toolbox.
8. You do not need to submit results of your work for this section of the assignment. You will rely on
the skills you learned in this section, however, to complete the ‘on your own section’ that follows.
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Section 2: On Your Own
In this part of the assignment you will use the knowledge and skills you have learned so far in this and
other assignments to perform a simple raster data analysis. You will determine possible locations for a
strawberry farm based on the set of predefined criteria. Datasets you will be working with are located
in T:\Class\Geography\geog303\Assignment 7 folder.
The Problem
As a co-op student working for the Enterprise Saskatchewan, a provincial government agency tasked
with encouraging and supporting business development in Saskatchewan, you are asked to determine
the most suitable sites in the province for locating a strawberry farm. The sites must be:
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In an area that is sufficiently high above the sea level and would not be at risk of frequent
flooding. The acceptable elevation is determined to be more than 500 meters above the sea
level.
Close to a major city to ensure the quick access to the market for this perishable produce. The
distance of 50 km or less was found to be acceptable.
Farms should not be located on moraines as it will make looking after and harvesting
strawberries difficult.
The farm should be located in an area where soil is suitable for agriculture.
Instructions
1. If necessary, start ArcMap and add the data from the Assignment 7 folder to map document. This
folder contains the following files:
lrgcity_lcc1 – a dataset containing municipal boundaries of Saskatchewan large cities (not
including major water bodies)
moraines_lcc – a dataset containing location of moraines
agric_lcc – a dataset showing classification of soils based on their ability to support agriculture
dem_sk_lcc – a dataset digital elevation model for Saskatchewan
2. Examine the data you just added and describe the datasets using the table below. This will help you
to get a better idea what kind analysis you can perform on the datasets and whether you would
need to transform them before that.
Submit the table describing the data
Dataset
Projection and
coordinate system
Data model
2 marks
Feature type
(if applicable)
Cell size (if
applicable)
Type of values
stored (if raster)
lrgcity_lcc1
moraines_lcc
agric_lcc
dem_sk_lcc
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Note that the large cities dataset includes some unconventional large cities in it. This illustrates the
issue of data quality when dealing with free digital data even if it is obtained from reputable
sources. For the purposes of this exercise, we will leave this issue unaddressed.
3. Before you start the analysis, you need to develop a ‘workplan’ determining the sequencing of your
operations. You can use the flowcharting approach you have seen used in the ModelBuilder. Based
on what you learned in the guided tutorial, think about what operations need to be done first to
provide inputs for further analyses. You may create a draft workflow chart now and refine it later
after you have a better idea about the specific steps.
Hint: this problem is solved using two main steps – transforming the data and then integrating the
transformed data sets to find the answer.
Submit a flowchart showing the workflow in your analysis
5 marks
4. Another step you need to do before starting to work with your data is to set the geoprocessing
environment. In the Environment Settings dialogue box, set the parameters as follows:
Current workspace
Scratch workspace
Output coordinates
Processing extent
Cell size
the folder where your input data is stored
the folder where you would like to keep your output datasets
Same as layer dem_sk_lcc
Same as layer dem_sk_lcc
Same as layer dem_sk_lcc
5. You will start your analysis with finding the areas of the province that are at the elevation of more
than 200 meters above the sea level using the Greater Then tool. Examine the output dataset after
it is added to the map document. Based just on this criterion, where the potential sites for a
strawberry farm are located?
1 mark
6. Next you will find which areas are within 50 km distance from a major city using the Buffer tool from
the Proximity set of the Analysis toolbox. Set the parameters as follows:
Linear unit
Distance
Dissolve Type
kilometres
50
All
Why did you need to use a tool from the Analysis tool box and not from a toolbox that is part of the
Spatial Analyst extension?
1 mark
7. Since the buffer dataset you just created in the previous step is a vector dataset, you will need to
convert it to the raster format. Open and examine the attribute table of this dataset. It contains
one polygon entity. Note that all attribute values for this entity are set to zero (this is the default
setting for the first entity in any dataset). This will create a problem when you will try to convert the
polygons in this dataset to raster as in the raster world zero values may be understood as the
NoData category. You will need to change the value ‘zero’ in the Id field to ‘one’ in order to be able
to perform the conversion.
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At the top of the ArcGIS window locate the Editor Toolbar button that looks like this
and press
it to open the Editor Toolbar. Click Editor  Start Editing. In the dialogue box that opens, select
the name of the buffer dataset and click OK to make it editable. Open the attribute table of the
buffer dataset, click in the Id cell that contains ‘0’ and type ‘1’ instead. Next click the Editor option
on the Editor Toolbar and choose Stop Editing. Choose ‘yes’ when prompted whether you want to
save the edits. Close the attribute table and close the Editor Toolbar. Now you are ready to convert
the buffer dataset to the raster format.
From the Conversion Tools toolbox call up the To Raster  Polygon to Raster tool. In the dialog
box that opens, set the following parameters leaving everything else at default:
Value field
Id
8. Next you will convert the moraine dataset to the raster format. What tool do you need to use?
Hint: set the value field parameter to Type
1 mark
9. Now examine the agric_lcc dataset. The class values in this dataset correspond to:
Class 1 – Soils with no limitations affecting their use for crops
Class 2 – Soils with moderate limitations which may restrict the range of crops or require some
(moderate) conservation practices
Class 3 – Soils with moderately severe limitations which may restrict the range of crops or
require special conservation practices
Class 4 – Soils with severe limitations which restrict the range of crops, or necessitate special
conservation practices, or both
Class 5 – soils with very severe limitations which are best suited to the production of perennial
forage crops; improvement practices are feasible
Class 6 – Soils with extremely severe limitations which are capable only of producing native
perennial forage crops; improvement practices are not feasible
Class 7 – soils with no capability for arable farming or permanent pasture
Class O – organic soils (not rated in capability classification)
We will assume that only soils in Classes 1 and 2 as suitable for our purposes.
You will use the Raster Calculator to select these two soil classes from the agric_lcc dataset and
save them into a separate dataset.
What tool or operator did you use to perform this operation?
1 mark
The output data set has the two classes as separate categories, whereas for the purposes of this
assignment it is not important to know that the soil belongs to a specific class, just that it belongs to
one of the two suitable classes. To get read of the additional information, you will reclassify values
in this dataset from ‘1’ and ‘2’ o just ‘1’ using the Reclassify tool.
10. Now you are all set for the next stage in our analysis. You have four datasets that satisfy the criteria
specified for potential locations of a strawberry farm. Next step is to combine them into one
dataset that will clearly show the answer to question stated at the beginning of this exercise.
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Recall that the desirable sites need to be located in areas safe from flood AND close to large cities
AND have soils suitable for agriculture. They also should NOT be on a moraine.
First you will combine the datasets that contain the first three criteria, between which a logical
relationship AND exists. You will use the Raster Calculator to multiply values in these datasets.
Can you explain why are we using this method to combine the datasets? What other tools could be
used to perform the same operation?
4 marks
What is the equivalent of this operation among the vector overlay tools?
Hint: consider only polygon-on-polygon options
2 marks
The output dataset created as a result this calculation contains two values – ‘1’ and ‘0.’ To make
further analysis run smother, reclassify these values as follows: ‘1’ to ‘1’ and ‘0’ to ‘NoData.’
The output of the reclassification shows all possible locations in Saskatchewan where the three first
criteria are met, i.e., these are areas located more than 500 meters above the sea level, close to
large cities and that have soils suitable for agriculture.
11. What is left in the analysis is to eliminate from this set of areas those that happen to be located on a
moraine. To do that you need to create a mask from the ratsrized moraines dataset by reversing
values in its cells. Those cells that contain value ‘1’ need to be reclassified to ‘NoData’ and those
that hold ‘NoData’ value need to be reclassified to ‘1’. The reclassification will allow you to erase
the areas that do not satisfy the last condition (are on the moraine) when you combine the results
of your previous analysis with the moraines mask.
After you created the mask, use the Raster Calculator to combine the two datasets.
What tool or operator have you used?
What is the equivalent of this operation among the vector overlay tools?
1 mark
2 marks
12. FINALLY, prepare a map showing results of your analysis using LetterPortrait template.
To make the map more informative, add the province outline (province.shp) from the Assignment 3
folder to your map document.
In the Table of Contents, change the name of the final output dataset to ‘Results of the Analysis’ and
the class label to ‘Potential sites.’
If the legend appears too small, you can adjust its size by selecting it and dragging on its corners
until it reaches the desired size.
You can change the scale bar units to ‘kilometres’ by clicking on the scale bar and making this and
other adjustments in the dialogue box that opens.
Title you map accordingly.
Submit a map showing results of your work
5 marks
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